1. Field of the Invention
The present invention relates to a mechanism with a torque-limiting device for controlling a rearview mirror.
2. Description of the Prior Art
A device is known for controlling a vehicle rearview mirror, in which the mirror is fixed on a supporting member mounted for pivoting about two perpendicular axes on a yoke integral with a casing mounted in a cup-shaped member. The casing contains two pinions which are driven in rotation by driving members. Furthermore, the pinions are each provided with a central hole in which is engaged the threaded part of a tubular element integral with control members hinged on the rear face of the mirror supporting member in order to communicate a pivoting movement to the mirror supporting member about the two perpendicular axes.
In this device, the pinions being driven in rotation by electrical motors, it is necessary to provide a torque-limiting mechanism in order to allow the threaded portion of the control member to disengage from the tapped hole provided in the pinions whenever a pressure is applied axially on the control members by pushing or pulling, especially when the mirror comes to a stop at the end of a stroke.
Additionally, as the pinions are mounted on the base-plate by means of a screw and washer, permanent alignment of the pinion axis relative to the control member axis is prevented, thus, producing a strong mechanical resistance. This particular type of connection results in the added disadvantage of presenting an axial play which, even though very small, generates a vibration of the mirror and gives shaking images.
It is also known from French Pat. No. 79 24114 to produce a mirror controlling device whose object is to obtain an alignment of the transmission axis of the control device.
This particular embodiment, however, requires extremely narrow production tolerances between the different elements. The elements with very strict tolerances are numerous and include endless screw wheels which are mounted inside upper and lower casings to allow the rotation of the screws resting on the bottom of the lower casing by a semi-spherical bottom and by a sliding surface of shape corresponding to a curved surface situated on the lower part of the screws. This obviously gives rise to major manufacturing difficulties.